drm: fix MMU dependencies

DRM_VM and DRM_LEGACY shouldn't be selected if MMU isn't set.

Fixes: 62a0d98a188c ("drm: allow to use mmuless SoC")
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1484211456-5759-1-git-send-email-benjamin.gaignard@linaro.org

drivers/gpu/drm/Kconfig

@@ -138,7 +138,7 @@ config DRM_KMS_CMA_HELPER
 
 config DRM_VM
 	bool
-	depends on DRM
+	depends on DRM && MMU
 
 source "drivers/gpu/drm/i2c/Kconfig"
 
@@ -267,7 +267,7 @@ source "drivers/gpu/drm/meson/Kconfig"
 
 menuconfig DRM_LEGACY
 	bool "Enable legacy drivers (DANGEROUS)"
-	depends on DRM
+	depends on DRM && MMU
 	select DRM_VM
 	help
 	  Enable legacy DRI1 drivers. Those drivers expose unsafe and dangerous